Abstract
We present sphere-on-ice friction experiments as a function of temperature, contact pressure, and speed. At temperatures well below the melting point, friction is strongly temperature dependent and follows an Arrhenius behavior, which we interpret as resulting from the thermally activated diffusive motion of surface ice molecules. We find that this motion is hindered when the contact pressure is increased; in this case, the friction increases exponentially, and the slipperiness of the ice disappears. Close to the melting point, the ice surface is plastically deformed due to the pressure exerted by the slider, a process depending on the slider geometry and penetration hardness of the ice. The ice penetration hardness is shown to increase approximately linearly with decreasing temperature and sublinearly with indentation speed. We show that the latter results in a nonmonotonic dependence of the ploughing force on sliding speed. Our results thus clarify the complex dependence of ice friction on temperature, contact pressure, and speed.
4 More- Received 17 July 2020
- Revised 30 October 2020
- Accepted 9 December 2020
DOI:https://doi.org/10.1103/PhysRevX.11.011025
Published by the American Physical Society under the terms of the Creative Commons Attribution 4.0 International license. Further distribution of this work must maintain attribution to the author(s) and the published article’s title, journal citation, and DOI.
Published by the American Physical Society
Physics Subject Headings (PhySH)
Viewpoint
A Penetrating Look at Ice Friction
Published 8 February 2021
A new approach for studying friction on ice helps explain why the ease of sliding depends strongly on temperature, contact pressure, and speed.
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Popular Summary
Ice friction—critical to winter sports, glacier movement, and transportation risks—is generated by an interface that includes many discrete contact points due to the surface irregularities on the ice and slider. Understanding how this extended interface impacts the slipperiness of ice is a major scientific challenge that remains difficult to address because the interface is buried between two bulk materials. We have overcome this challenge and discovered that ice friction is low because of mobile ice molecules at the surface, whose mobility—and thus slipperiness—can be suppressed by a high contact pressure or a low temperature.
We use a novel combination of experimental and numerical techniques to enable a rich understanding of the interplay between local contact pressure, sliding velocity, ice temperature, and ice friction. In our experiments, we drag various sliders over an ice surface at varying speeds, all the while tracking the forces on the object and the ice temperature. Close to the melting point, we find that the slipperiness is disrupted by a plastic deformation of the ice surface, controlled by the hardness of the ice and the surface geometry, which results in a sharp increase of friction.
We conclude that it is the high mobility of molecules in the outermost layer of the ice combined with the exceptional hardness of ice close to its melting point that cause its slipperiness. Ice friction can be minimized by curtailing the contact pressure, a factor already controlled by ice skaters: The optimal ice skate has a smooth bottom (low pressure) for low friction and sharp edges (high pressure) for grip.